The present invention relates to a hydraulic control system and method for a belt-drive continuously variable transmission (CVT).
One example of such a hydraulic control system is known, which includes an oil pump and a pressure regulator valve coupled with the oil pump. The pressure regulator valve adjusts a hydraulic pressure as a pulley clamping pressure which is discharged from the oil pump. A clutch regulator valve disposed on the downstream side of the pressure regulator valve adjusts a hydraulic pressure to be supplied to a select switching valve. A torque converter regulator valve disposed on the downstream side of the clutch regulator valve adjusts a hydraulic pressure to be supplied to a lockup control valve. An oil cooler for maintaining oil at a constant temperature is disposed on the downstream side of the torque converter regulator valve. A lubricating oil supply member, for example, an oil supply nozzle, for supplying the oil for lubricating the belt of the CVT is disposed on the downstream side of the oil cooler. In the belt-drive CVT, an oil amount leaking from lubrication parts of the CVT increases under high oil temperature condition. This will prevent the oil from being supplied in a sufficient amount through the oil supply nozzle. In order to maintain a required flow amount of the belt lubricating oil at high oil temperature, a conventional art controls oil pump speed, namely, engine speed, by controlling a transmission ratio of the CVT based on a predetermined flow amount of the oil discharged from the oil pump which is set corresponding to each oil temperature.